If looking for a small apt. In the Thonglor area, I recommend Mintsstudio. The location great, right on Sukhumvit at the BTS Station.. the studio is pretty large, well furnished with a comfortable Queen bed.
The building is a modern high rise, with 24 hr security. Building has a nice pool long enough to do laps, and a decent, not great, gym. The cardio machines good, but the bikes and exercise machines pretty cheap and not well maintained.
There is a small alley full of street food off Soi 38, and Thonglor Soi 55 has many restaurants.
The owner was very responsive and helpful.